Optical inspection of container finish dimensional parameters

ABSTRACT

Apparatus for inspecting external dimensional parameters of a container finish that includes a light source for directing light energy onto the finish of the container and a matrix array sensor disposed to receive an image of the container finish illuminated by the light source. A telecentric lens is positioned to focus onto the matrix array sensor an image of the container finish profile formed by light energy traveling parallel to the telecentric lens axis, such that the finish profile appears as a dark image against a light background at the sensor. The matrix array sensor is scanned at increments of container rotation to determine one or more dimensional parameters of the container finish.

The present invention is directed to non-contact measurement ofcontainer dimensional parameters, and more particularly to an apparatusand method for optical measurement of external dimensions of a containerfinish profile.

BACKGROUND AND SUMMARY INVENTION

In the art of container manufacture, the term "container finish"generally refers to that portion of the container that defines thecontainer mouth. In a bottle, for example, the finish includes thatportion of the container neck having threads and/or shoulders forreceiving the container cap, as well as the upper surface of the necksurrounding the container mouth against which the cap seats. It isimportant that the container finish be properly manufactured and possessdesired external geometric characteristics so that a cap may be affixedthereto to seal the container against leakage and escape of carbonationduring handling and storage.

U.S. Pat. No. 4,701,612, assigned to the assignee hereof, discloses amethod and apparatus for inspecting the finish of transparentcontainers, particularly glass containers, which include facility fordirecting diffused light energy laterally through the container finishas the container is rotated about its central axis. A camera includes aplurality of light sensitive elements or pixels disposed in a lineararray angulated with respect to the container axis and coplanartherewith to view the external and internal wall surfaces, the latterthrough the open container mouth. Individual elements of the cameralinear array are sampled by an information processor at increments ofcontainer rotation, and corresponding data indicative of light intensityat each element is stored in an array memory as a combined function ofelement number and scan increment. Such data is compared followingcompletion of container rotation to standard data indicative of anacceptable container finish, and a reject signal is generated if suchcomparison exceeds an operator-adjustable threshold.

U.S. Pat. No. 4,958,223, also assigned to the assignee hereof, disclosesa method and apparatus for inspecting the finish of a container as thecontainer is held and rotated about its central axis. A light source ispositioned to direct diffused light energy onto the container finish,and a camera is positioned across the axis of the container from thelight source. The camera comprises a matrix array sensor positioned withrespect to the camera focusing elements to receive an image of thecontainer finish as illuminated by the light source. Informationprocessing electronics are coupled to the camera array for indicatingoptical characteristics of the container finish as differing functionsof light intensity incident on the matrix elements for detectingstructural commercial variations or geometric parameters of thecontainer finish.

Although the systems so disclosed in the noted patents representsignificant advances as compared with previous finish inspectiontechniques, further improvements remain desirable. For example, inapplications in which it is specifically desired to measure externaldimensional parameters of the container finish, as opposed for exampleto internal structural variations in the container finish area, it ishighly desirable to develop a sharp image of the containerprofile--i.e., an image in which transition at the profile edges ischaracterized by high contrast and sharp transition between light anddark. A general object of the present invention is to provide a systemand method that is characterized by such a sharp transition at theprofile image edges, and thus are adapted for obtaining improved andenhanced measurement accuracy of finish profile dimensional parametermeasurements.

Apparatus for inspecting external dimensional parameters of a containerfinish in accordance with the present invention includes a light sourcefor directing light energy onto the finish of the container and a matrixarray sensor disposed to receive an image of the container finishilluminated by the light source. A telecentric lens and camera lenscombination is positioned to focus onto the matrix array sensor an imageof the container finish profile formed by light energy travelingparallel to the telecentric lens axis, such that the finish profileappears as a dark image against a light background at the sensor. Thematrix array sensor is scanned, preferably at increments of containerrotation, to develop multiple electronic two-dimensional images of thefinish profile, each from a different azimuthal position with respect tothe finish, from which one or more dimensional parameters aredetermined. Use of the telecentric lens arrangement effectively toreject light rays that are non-parallel to the optical axis of the lensand camera provides an image of the container finish that ischaracterized by high contrast between the dark image and the lightbackground, and a sharp non-ambiguous transition at the profile edges.

BRIEF DESCRIPTION OF THE DRAWING

The invention, together with additional objects, features and advantagesthereof, will be best understood from the following description, theappended claims and the accompanying drawing in which:

FIG. 1 is a schematic diagram of an electro-optical non-contact systemfor measuring external dimensional parameters of a container finish inaccordance with a presently preferred embodiment of the invention; and

FIG. 2 is a schematic diagram of the container finish profileillustrating exemplary dimensional parameters that can be measured inaccordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates an apparatus 10 for measuring dimensional parametersof the finish 12 of a container 14 in accordance with a presentlypreferred embodiment of the invention. A light source 16 is disposed todirect light energy onto the container finish from a direction generallyorthogonal to the container axis. Light source 16 may comprise one ormore lamps and a diffuser of limited width, or more preferably maycomprise a single lamp 18 disposed at the focus of a lens 20 fortransmitting substantially parallel light rays onto container finish 12.Light source 16 may be of constant illumination or strobed. A camera 22is positioned across container 14 from light source 16. Camera 22includes a matrix array CCD sensor 24, an entrance pupil 26 and lenses28,30 associated with entrance pupil 26.

A telecentric lens 32 is positioned between camera 22 and containerfinish 12. Telecentric lens 32 has a first focus in the direction ofcontainer 14 at infinity, and a second focus at entrance pupil 26. Thatis, camera 22 is positioned with respect to lens 32 so that entrancepupil 26 is spaced from lens 32 by the focal distance of the lens. Thus,pupil 26 with lenses 28,30 functions as an iris in combination with lens32 for focusing onto sensor 24 essentially only light rays from lightsource 16 that travel past finish 12 parallel to the optical axis oflens 32 and camera 22. That is, light rays that impinge upon container14 are reflected, absorbed and/or refracted, so that the light rays donot emerge from the container in a direction parallel to the lens/cameraaxis. Camera 22 is positioned such that sensor 24 is at the image of thecontainer finish as seen through telecentric lens 32. Thus, sensor 24receives a sharp image of the container finish profile formed as a darkimage against a light background.

A conveyor 34, typically including a starwheel (not shown) and a slideplate 27, is so disposed and connected to a source of molded containersas to bring successive containers 14 into position at apparatus 10.Conveyor 34 may be of any suitable type, such as those shown in U.S.Pat. Nos. 4,230,219 and 4,378,493. Successive containers are held infixed position and rotated by a device 36, such as a drive roller, aboutthe central axis of the container. An encoder 38 is coupled to thecontainer rotation mechanism to provide signals indicative of incrementsof container rotation. An information processor 40 is coupled to encoder38 and to matrix array sensor 24 for scanning the sensor at incrementsof container rotation and developing multiple two-dimensional electronicimages of the container finish from different azimuthal positions withrespect to the finish. As an alternative to use of encoder 38,information processor 40 may be controlled to scan sensor 24 atsubstantially equal increments of time while container 14 is rotated atsubstantially constant velocity.

There are thus developed at information processor 40 multipletwo-dimensional electronic images of the container finish, asillustrated schematically at 42 in FIG. 2. Such images may be displayedat 44 (FIG. 1) and/or analyzed using suitable techniques to generate acontainer reject signal in the event that one or more container finishdimensional parameters are unsatisfactory. Exemplary techniques forscanning matrix array sensor 24 and developing two-dimensionalelectronic images 42 of the container finish profile are disclosed inabove-noted U.S. Pat. No. 4,958,223.

FIG. 2 illustrates exemplary dimensional parameters of the containerfinish image 42 that may be measured and analyzed in accordance with thepresent invention. The dimensional parameters are designated by theGlass Packaging Institute Standard Code Letters A (bead diameter), D(crimping ledge height), E (thread base wall diameter), F (top and sideseal diameter), H (top to bead closure clearance) and T (threaddiameter). Other standard or non-standard parameters may also bemeasured. Since the container finish refracts, reflects and/or absorbslight from source 16 that impinges on the container, so that any lightrays that emerge from the container will not be parallel to the opticalaxis of lens 32 and camera 22, and thus not directed onto sensor 24, theedge contrast at image 42 between the dark profile of the containerfinish and the light background is very distinct and sharp. Thus,container finish dimensional parameters are measurable withsignificantly increased accuracy and precision as compared with priorart technique heretofore proposed.

I claim:
 1. A method of inspecting external dimensional parameters of atransparent container finish that comprises the steps of:(a) directingcollimated light energy onto the exterior of the finish of a transparentcontainer such that a first portion of such light energy travels pastthe finish exterior while a second portion is incident on the finishexterior and reflected or refracted by the container finish such thatlight rays in said second portion are no longer parallel to collimatedlight rays in said first portion, (b) focusing through an iris onto amatrix array sensor said first portion of said collimated light energythat travels past the container finish exterior in a direction parallelto an optical axis of said sensor, and thereby excluding from lightenergy focused onto said sensor said second portion of said collimatedlight energy that is reflected or refracted by the container finish,such that the exterior profile of the container finish appears at saidsensor as a dark image against a light background, (c) scanning saidmatrix array sensor to obtain a two-dimensional image of the exteriorprofile of the container finish, and (d) determining at least oneexterior dimensional parameter of the container finish from saidtwo-dimensional image.
 2. The method set forth in claim 1 comprising theadditional step of (e) rotating the container about its axis, andwherein said step (c) comprises the step of scanning said matrix arraysensor at increments of container rotation so as to develop multipletwo-dimensional images of the container finish exterior profile atincrements of container rotation from different azimuthal positions withrespect to the finish.